Automated material handling and sortation systems are known for receiving, transporting and discharging goods among various stations in large scale sortation operations, for example warehousing, distribution, postal sortation and handling of mail and packages, and airport baggage handling, to name a few. Whatever the operation, goods typically originate from one location within the facility and must be sorted and transported to several different locations for further handling, or originate from several locations within a facility and must be transported to a single location such as a shipping dock. The manner in which the goods are sorted and selectively distributed among various stations in a facility of course depends on the nature of the operation.
One known sortation and delivery method involves using powered belt or roller conveyers to transport individual items or sorted loads of items to various destinations within a facility. When goods from multiple sources must be delivered to a single station, associated take away conveyors must be merged onto a main conveyor or discharge point. This requires careful coordination of each item as it arrives to prevent jams or damage. Each merge point on such a conveyor system would accordingly require a complex system of sensors, start/stop controls, actuators, power supply lines, etc. Similarly, when items must be delivered to multiple destinations or stations in a facility, a main conveyor must be provided with diverter apparatus to direct individual items or batches of items to either continue or be diverted at various points. Each diverter apparatus would require an additional closed system including sensors, actuators, control mechanisms, wiring and power supply to accomplish the diverting operation and track and identify the items being diverted.
The disadvantages of conveyor-type systems have led to the development of tracked systems. In one known type of system, a closed loop track carries cars propelled by a continuous belt or chain drive. The cars are equipped with open trays which can be loaded from chutes, and subsequently tilted to unload their carloads into bins which are located around the track. These cars are often termed "dumb" because they do not initiate any sorting actions, but rather respond to stimuli from the induction stations to discharge their load. For example, car speed is controlled by a track-side motor which circulates the belt or train drive, and car dumping is controlled by track-side dumping mechanisms. Such systems are designed for long term installations which sort and transport large volumes of goods. Although these closed loop track systems are an improvement over conveyor-type systems, the complexity of their track, drive and tilting mechanisms makes it a major undertaking to set them up or rearrange their sortation layout. They must be shut down for nearly all maintenance tasks.
An improvement over continuous belt or chain drive closed loop track systems is disclosed in U.S. Pat. No. 5,018,928 to Hartlepp. Hartlepp discloses a train-type automated track sortation system, including a number of "smart" cars and a locomotive or tug for pulling the cars around the track between various discharge and induction stations. The cars on the train are loaded with goods to be sorted or delivered and given destination addresses for the goods at an induction or loading station. Once a train has left the loading station, functions such as keeping track of position, regulating speed and dumping cars are controlled by a microprocessor placed aboard each locomotive. This design allows the track to be simplified as it need only provide a path and power supply for the train (or trains) running between discharge stations positioned along the track. There is accordingly no drive train, drive motor or track-side dumping control mechanisms with attendant wiring required. The track design allows new track configurations to be made up by simply adding track switches, added track sections and discharge stations. Sorting capacity can be varied by adding or subtracting cars to a train in accordance with the capacity of the loading station, or by changing the number of trains operated on a track. It is also possible to perform many maintenance tasks by removing individual cars or trains from the track, leaving the rest of the system intact and operating.
The Hartlepp cars utilize a mechanical tipping mechanism with a computer-controlled tipping arm selectively activated to engage off-track tip actuating structure to initiate a discharge at a discharge station when the train passes. This occurs while the car and train are moving. As a car with a load to be discharged passes the appropriate discharge station, the tipping mechanism is activated to engage an actuator on the track to tilt a tray carrying the load to either side of the track where the discharge station is located.
Despite the advantages of the Hartlepp apparatus over conveyor-type and belt- or chain-driven track systems, there are some drawbacks. The Hartlepp system requires frequent communication between a central off-track computer which monitors and controls induction and discharge operations, and the train. Goods are received by the train at a "master" loading station with centralized PLC control. Destination information is fed from the central computer to the locomotive, which dumps packages from each car at the appropriate discharge stations. Since loading and discharge of packages to and from the cars on the train is centrally monitored and controlled by a host computer's instructions to the locomotive and induction stations, there is no communication between the induction and discharge stations and the train. If events at the stations would prevent a proper induction or discharge, or if the central computer's tracking of the items and station capacity is incorrect, or if the central computer is "down", there is no way for the train to accurately monitor and control its own operations with track-side devices on a local level. This can result in discharge malfunctions, overloaded trains, damage to packages or items being sorted, and general loss of control over the system.